Cover block :Add back missing styles (#38362)

* Add back missing styles to ensure existing cover blocks show correction dimRatio
Co-authored-by: Glen Davies <glen.davies@a8c.com>

packages/block-library/src/cover/style.scss

@@ -70,6 +70,19 @@
 		opacity: 0.5;
 	}
 
+	// The following styles are needed to support legacy blocks added prior to the update
+	// that moved opacity to a nested span.
+	// https://github.com/WordPress/gutenberg/pull/35065
+	// https://github.com/WordPress/gutenberg/pull/38362
+	@for $i from 1 through 10 {
+		&.has-background-dim.has-background-dim-#{ $i * 10 } {
+			&:not(.has-background-gradient)::before,
+			.wp-block-cover__gradient-background {
+				opacity: $i * 0.1;
+			}
+		}
+	}
+
 	@for $i from 0 through 10 {
 		.wp-block-cover__gradient-background.has-background-dim.has-background-dim-#{ $i * 10 } {
 			opacity: $i * 0.1;